1. Field of the Invention
The present invention relates to an improved spring made from a synthetic resin which is developed for a mattress and is also applicable as other cushioning elements and elastic elements, and to a spring assembly for a mattress using the springs.
2. Description of the Prior Art
As a mattress for bedding such as a bed, there has been employed a spring assembly of a type in which a number of metal coil springs, metal torsion bars or the like are flatly, uniformly distributed and in such a state, upper and lower edges of adjacent ones thereof are flatly joined to each other and an outer peripheral edge of the spring assembly is surrounded by a wire rod or the like. Such a spring assembly, however, is generally disadvantageous in that the complicated structure leads to the poor productivity; a lot of labor is required to handle the heavy spring assembly upon transportation or the like thereof; creak and rust occur in service thereof; and the spring assembly is poor in matching with a fiber material such as a wrapping texture.
To cope with these inconveniences, studies have been made to develop, as an alternative of the conventional metal spring, a plastic spring having merits of reducing the weight, eliminating occurrence of noise, and enhancing the productivity. Such a plastic spring can be formed into a shape quite different from that of the conventional metal spring by making use of a molding process generally adopted for forming plastic products. With such a geometrical effect, a plastic spring is allowed to ensure dynamic characteristics being large enough to compensate for the poor strength of a plastic material used for the plastic spring.
The above-described plastic spring, however, has a problem that when the spring is elastically deformed up to a critical geometry caused by an excessive compressive load applied thereto, the supporting state of the spring may become unstable due to the poor strength of the plastic material, and at the worst case, there occurs breakage of the spring.
With respect to a spring assembly for a mattress using a number of single plastic springs, it is expected to develop a new structure having merits in terms of material and manufacturing technique thereof.